To provide information on the basic process of ATP-transphosphorylation, studies are being conducted: (a) To continue the comparison of the isoenzymes from calf, rabbit, and man of ATP-creatine transphosphorylase, by physical, chemical and kinetic means; (b) To shed light on the basic structures of the intact two-chain molecule of the ATP-creatine transphosphorylases, with especial attention to the hybrid species; (c) To elucidate the primary structures of the ATP-creatine transphosphorylases (brain- and muscle-type), and of the ATP-AMP transphosphorylases from the muscle and liver of rabbit and calf; (d) To correlate chemical structure and enzyme function of the ATP-creatine transphosphorylases and of the ATP-AMP transphosphorylases, especially with the aid of immunological probes; (e) To complete the comparison of the ATP-creatine transphosphorylases isolated from dystrophic tissues with their normal human counterparts, and to explore with immunological assays the isoenzymic distribution during embryogenesis, and thereby to provide clues as to the nature of this disorder; (f) To re-exlore the association-dissociation behavior of the NTP-NDP transphosphorylase (nucleoside diphosphokinase) with attention to effects on enzyme kinetics and covalent (phosphoryl) intermediates. As part of a program on NADP-associated reactions: (a) A number of physiochemical properties of the crystalline NADP-enzyme compound have been compared with the NADP-free crystalline glucose 6-phosphate dehydrogenase from brewers' yeast. Studies on the ligand-induced association phenomenon have been extended to its other substrates. The controlled use of EDTA 3 which modifies the dissociation-association equilibria of the enzyme has permitted a simplified approach to studies on the catalytic mechanism through direct steady-state kinetic measurements on the active, two-chain enzyme species. Studies are in progress which may correlate physical changes (the association-dissociation behavior) with enzyme function and its essential side-chain groups with catalytic activity and substrate binding, (b) Studies on ale-yeast NADPH-cytochrome C reductase are being continued.